Bushing arrangement

ABSTRACT

A bushing arrangement for passing at least one electrical cable with conductive shielding through an opening in a wall while providing protection against electromagnetic overtension or electrical interference comprising an electrically conductive bushing in the wall opening that is electrically connected to earth ground potential, and electrically connecting an electrically conductive tape between the electrically conducting shielding and the electrically conductive bushing so as to connect the conductive shielding to earth ground potential.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation of International ApplicationNo. PCT/NL01/00594, filed Aug. 8, 2001, which claims the benefit ofNetherlands Patent Application No. 1015895, filed Aug. 8, 2000.

BACKGROUND OF THE INVENTION DETAILED DESCRIPTION OF PREFERREDEMBODIMENTS OF THE INVENTION

[0002] The invention relates to a bushing arrangement for passing atleast one cable through an opening in a wall, plating, partition and thelike (such as a bulkhead of a ship, for example) whilst providingprotection against electromagnetic overtension and/or interference.Hereinafter, the term “wall” will be used for the sake of simplicity,whilst said term is understood to include other partitions as well.

[0003] Such a bushing arrangement is disclosed in Dutch patentapplication no. 1011718 in the name of the present applicant. Thebushing arrangement that is disclosed therein consists of a steelbushing arrangement fitted in a wall opening, through which a number ofsingle-core or multiple-core cables are passed. The cables are strippedof their sheathing along a suitable part of their length, so that saidcables can locally come into electrically conductive contact with theirenvironment. The longitudinal parts of the cables are then embedded inan electrically conductive moulding paste so as to effect electricalconduction between the cables and the bushing arrangement, after whichthe wall opening is filled up with a suitable sealing compound. A rubberhose member may be fitted round each cable before the moulding paste isprovided, whilst any remaining space in the wall opening will be filledwith the similar hose members. One drawback of the bushing arrangementthat is disclosed in the aforesaid Dutch patent application is the factthat it has become apparent in practice that in some cases the mouldingpaste exhibits a relatively high electrical resistance value, in theorder of about 100-100 Ohm, after curing. In particular this means thatthe degree to which electricity can flow away to earth or ground via themoulding paste has decreased considerably, which has an adverse effecton the extent of protection that is provided against electromagneticovertension. The same applies, mutatis mutandis, as regards (theprotection against) electromagnetic interference.

[0004] The object of the invention is to improve the bushing arrangementthat is known from the prior art, in the sense that there is proposed ahigh-grade fire resistant, gastight and liquid-tight bushing arrangementwhich is furthermore optimally protected against electromagneticovertension and/or interference.

[0005] In order to accomplish that objective, a bushing arrangement ofthe kind referred to in the introduction is characterized in the saidbushing arrangement comprises an electrically conductive tape, which isin contact with an electrically conductive cable shielding of the atleast one cable being passed through and which functions to earth thecable shielding.

[0006] Electrical installations and machines, which usually includehighly sensitive components, for example for control and registrationpurposes, can easily experience interference caused by various externalelectromagnetic (em) fields and pulses. Such electromagnetic fields andpulses may have been generated by radar installations, thunderstorms,nuclear explosions and electrical equipment, for example. A measure thatis frequently used in practice for reducing such interference is theprovision of a steel structure, which functions as a Faraday cage, roundthe space that is intended for electronic equipment. Electrical cablesthat are passed into such a screened space can conduct undesirableelectromagnetic fields and pulses into the electronic equipment,however. Such conduction will generally take place over the electricallyconductive shielding (braid) of the respective cables that are passedthrough.

[0007] According to the invention, the external undesirable em fieldsand pulses will flow away to earth along the electrically conductiveshielding of a cable being passed through, via the electricallyconductive tape. In particular, the electrically conductive tape is atleast partially wound round the electrically conductive cable shieldingin the operative condition.

[0008] It is noted that within the framework of the invention the term“cable” is understood to include an electrically conductive conduit,tube, pipe or the like, for example a metallic tube or pipe, with thepresent tape being in electrically conductive contact therewith in theoperative condition.

[0009] In one preferred embodiment of a bushing arrangement according tothe invention, the electrically conductive tape is wound round theelectrically conductive cable shielding near its one end, whilst it isin electrically conductive contact with an electrically conductivebushing housing (made of a metal, for example) that is fitted in theopening in the wall. In another preferred embodiment, the earthing ofthe electrically conductive cable shielding is effected by means of theelectrically conductive tape by providing an electrically conductivematerial on at least one open side of the wall, which material is inelectrically conductive contact with the tape. The electricallyconductive material is at least substantially made up of several piecesof electrically conductive tape material, whether or not folded, whichhave been placed into the opening, and/or of several electricallyconductive sleeve means or hose members which have been placed into theopening, which hose members or sleeve means preferably extend in thesame direction as the at least one cable being passed through.

[0010] In another preferred variant, the electrically conductivematerial is the graphite-containing moulding paste that is known fromthe aforesaid Dutch patent application no. 1011718.

[0011] In another preferred embodiment of a bushing arrangementaccording to the invention, the electrically conductive tape and/or theelectrically conductive sleeve means is/are substantially made of anelectrically conductive rubber. The rubber has been made electricallyconductive by chemical means, in particular through the addition theretoof carbon particles, preferably in the form of carbon black. Inparticular, the rubber is EPDM rubber, whilst the carbon particles arepreferably concave shell-shaped, especially of the type “Ketjenblack EC”300J or 600 JD™ These existing types of carbon black known under thecommercial name of “Ketjenblack” have a unique morphology in comparisonwith conventional types of carbon black, which renders themexceptionally suitable for the present electrically conductiveapplication. The abbreviation EPDM stands forEthylene/Propylene/Diene/Monomer. It is noted that also other elastomersor plastomers can be used as materials for the tape and the sleevemeans.

[0012] In another preferred embodiment of a bushing arrangementaccording to the invention, the electrically conductive tape is a metaltape. Preferably, the electrically conductive (rubber or metal) tape isflexible, that is, deformable, so that it can readily be passed alongother cables that are passed through the bushing arrangement.

[0013] In another preferred embodiment of a bushing arrangementaccording to the invention, the electrically conductive tape has acontact width of at least about 20 mm, preferably about 40 mm. In thelatter case, the tape is usually used for civil applications(attenuation factor −30 dB), whilst a contact width of more than 100 mm(attenuation factor −60 dB) can be used for military applications. Bywinding the present tape of such width round the electrically conductivecable shielding, an optimum electrically conductive contact is effectedso as to prevent electromagnetic overtension and/or interference.

[0014] In another preferred embodiment of a bushing arrangementaccording to the invention, the remaining space in the wall opening isat least partially filled up with several fire resistant sleeve means,which extend in the same direction as the at least one cable beingpassed through. Possibly, each cable is passed through one of the sleevemeans thereby. The sleeve means or hose members are preferably dividedlengthways, so that, in the latter case, they can be fitted over thecables after the cables have been pulled through the bushingarrangement.

[0015] In another preferred embodiment of a bushing arrangementaccording to the invention, a heat resistant and/or liquid repellent(preferably expandable) putty is sealingly provided on at least one openside of the opening. The putty functions to enhance the gas tightnessand liquid tightness of the present bushing arrangement.

[0016] The invention furthermore relates to a method for passing atleast one cable through an opening in a wall and the like whilstproviding protection against electromagnetic overtension and/orinterference, using a bushing arrangement according to the invention,characterized in that in use an electrically conductive tape is broughtinto contact with the electrically conductive shielding of the at leastone cable being passed through for the purpose of earthing it.

[0017] The invention will now be explained in more detail with referenceto figures illustrated in a drawing, wherein FIGS. 1-8 are schematic,perspective views of various embodiments and illustrating successivesteps for providing a preferred variant of a high-grade fire resistant,gastight and liquid-tight bushing arrangement according to theinvention, which is furthermore optimally protected againstelectromagnetic overtension and/or interference.

[0018]FIG. 1 shows an opening in a wall 2, in which a steel bushinghousing 3 is mounted. For the sake of simplicity, only three multi-corecables 4, 5, 6 are shown in the drawing, which cables have each beenstripped of their plastic sheathing 7 along part of their length, sothat their electrically conductive shielding (braid) 8 is now exposed.In accordance with the invention, a tape 10 of EPDM rubber on a windingroll 9 is used, which tape has been made electrically conductive by thechemical addition thereto of carbon particles (for example carbon blackparticles), which tape is to be wound round the electrically conductivecable shielding 8. Tape 10 preferably has a width of 40 mm, so that anoptimum electrically conductive contact with the electrically conductivecable shielding 8 is realised. The electrical earthing is ensured bywinding tape 10 to a diameter larger than that of cables 4, 5, 6, as isshown in FIG. 1 and as will be explained in more detail yet.

[0019]FIG. 2 shows the situation of FIG. 1, with the understanding thata fire resistant (rubber) hose member 11, 12, 13 is fitted round eachcable 4, 5, 6 and that the provision of the tape 10 has been concludedby cutting tape 10 off the winding roll 9 and attaching the free end oftape 10 thus formed to the part of the tape 10 that has already beenwound round the cable by heating the free end. “Attachment” can also beeffected by binding a band or the like round the wound tape 10. In FIG.3, the remaining space of the bushing housing 3 in the wall opening 1 isfilled with fire resistant (rubber) hose members 14, which are identicalto hose members 11, 12, 13. Hose members 14 function as fillers,therefore. A bar-shaped element 15 shown in FIG. 4 (which may or may notbe made of an electrically conductive material) is inserted in one ofthe hose members 14 in order to make it possible to pass a new cablethrough the bushing housing 3 in place of the bar-shaped element in duecourse. Thus, the bar-shaped element 15 functions to determine thecorrect position for the new cable. Hose members 11, 12, 13, 14 areknown under the trade name “RISE” of the present applicant.

[0020] In FIG. 5, hose members 16 of an electrically conductive materialare disposed on one open side of wall opening 1, whilst it is alsopossible to use folded pieces 17 of tape 10 (FIG. 6) in addition to orinstead of the hose members. Since the hose members 16 are made of thesame electrically conductive material as tape 10, viz. EPDM rubber thathas been made electrically conductive by the addition of carbonparticles, the electrically conductive cable shielding 8 is in earthedconnection with steel bushing housing 3 via tape 10, hose members 16and/or pieces of tape 17. As already stated, tape 10 is wound to adiameter larger than that of the cable so as to ensure the electricallyconductive contact between tape 10 and hose members 16. Finally, a putty18 (which is known under the trade name “FIWA”) of the present applicantis sealingly provided on that side of the wall opening 1 (FIG. 7). It isalso possible, of course, to fit the hose members 16 and/or the piecesof tape 17 on either side of the wall opening 1. In particular tape 10and putty 18 provide an airtight seal of opening 1, thus preventingcorrosion of the electrically conductive cable shielding 8.

[0021] The present bushing arrangement is based on the use of two typesof hose members, therefore: hose members 11, 12, 13,14 of a fireresistant (non-vulcanized) rubber on the one hand (with hose members 11,12, 13 being fitted around cables 4, 5 and 6, respectively, and hosemembers 14 functioning as fillers), and hose members 16 of anelectrically conductive rubber material corresponding to that of tape 10on the other hand. It is also possible, of course, to form both types ofhose members of the electrically conductive rubber. In addition, it ispossible to use massive hose members 14, 16 of vulcanized rubber insteadof or in addition to the hollow hose members 14, 16. Such massive hosemembers in fact form bar material in that case.

[0022] From the figures it will be understood that the terms opening inthe wall, wall opening or the like as used herein, when used inconjunction with a bushing arrangement, are understood to mean theopening in the bushing housing, the bushing housing opening and thelike.

[0023] It is noted that the invention is not restricted to theembodiment as shown in the drawing, but, that it also comprises otherembodiments that fall within the scope of the appended claims.

1. A bushing arrangement for passing at least one electrical cablethrough an opening in a wall to provide protection against at least oneof electromagnetic overtension and interference, said busing arrangementcomprising: an electrically conductive tape substantially made of anelectrically conductive rubber by the addition thereto of carbonparticles in the form of carbon black; and an electrically conductivecable shielding of said at least one cable being in contact with saidelectrically conductive tape and functioning to connect said cableshielding to earth ground.
 2. A bushing arrangement according to claim1, wherein said electrically conductive tape is at least partially woundround the electrically conductive cable shielding in the operativecondition.
 3. A bushing arrangement according to claim 2, comprising: anelectrically conductive bushing housing fitted in the opening in saidwall; and said electrically conductive tape being wound around theelectrically conductive cable shielding to provide electrical contactbetween said cable shielding and said electrically conductive bushinghousing to electrically couple said cable shielding to earth ground. 4.A bushing arrangement according to claim 1, wherein said electricallyconductive material is provided on at least one side of said wallopening, said electrically conductive material being in electricallyconductive contact with said tape.
 5. A bushing arrangement according toclaim 4, wherein said electrically conductive material is at leastsubstantially made up of several pieces of electrically conductive tapematerial, whether or not folded, which have been placed into saidopening.
 6. A bushing arrangement according to claim 4, wherein saidelectrically conductive material is at least substantially made up ofseveral electrically conductive sleeve means which have been placed intosaid opening.
 7. A bushing arrangement according to claim 4, whereinsaid electrically conductive material is substantially made of anelectrically conductive rubber.
 8. A bushing arrangement according toclaim 7, wherein said rubber has been made electrically conductivethrough the addition thereto of carbon particles, preferably in the formof carbon black.
 9. A bushing arrangement according to claim 8, whereinsaid carbon particles are concave, shell-shaped particles.
 10. A bushingarrangement according to claim 8, wherein said carbon particles are ofthe type “Ketjenblack EC” 300J or 600 JD™.
 11. A bushing arrangementaccording to claim 7, wherein said rubber is EPDM rubber.
 12. A bushingarrangement according to claim 1, wherein said electrically conductivetape has a contact width of at least about 20 mm, preferably about 40mm.
 13. A bushing arrangement according to claim 6, wherein anyremaining space in said wall opening is at least partially filled withseveral fire resistant sleeve means extending in the same direction assaid at least one cable passed through said wall opening.
 14. A bushingarrangement according to claim 13, wherein said at least one cable ispassed through a fire resistant sleeve member.
 15. A bushing arrangementaccording to claim 13, wherein at least one of a heat resistant andliquid repellant putty is sealingly provided on at least one open sideof said wall opening.
 16. A method for passing at least one electricalcable having electrically conductive shielding through an opening in awall while providing protection against electromagnetic overtension orelectrical interference comprising the steps of: placing an electricallyconductive bushing in said opening that is electrically connected toearth ground potential; using an electrically conductive tape to connectsaid electrically conductive shielding to said electrically conductivebushing so as to connect said conductive shielding to earth groundpotential.